Continuous vacuum and inert gas process for treating titanium and other metals



Jan. 7, 1964 G. A. PAGONIS 3,116,998

CONTINUOUS VACUUM AND INERT GAS PROCESS FOR TREATING TITANIUM AND OTHER METALS Filed Dec. 31, 1959 5 Sheets-Sheet 1 HIGH VACUI/M ALLO N6;-

INERT' GAS VAC/111M PUR/FY/Nq- SHMPL/NG Teams/ m IN V EN TOR.

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-- ATTORNEYS Jan. 7, 1964 oms 3,116,998

CONTINUOUS VACUUM AND INERT GAS PROCESS FOR TREATING TITANIUM AND OTHER METALS Filed Dec. 31, 1959 5 Sheets-Sheet 2 H TTORNE KS 7, 1964 e. A. PAGONIS 3,116,998

commuous VACUUM AND INERT GAS PROCESS 31 QFOR TREATING TITANIUM AND OTHER METALS 195 5 Sheets-Sheet 3 Filed Dec.

l/ l/ I 0 INVFNTOR. George A. Pagoms BY rm/megs Jan. 7, 1964 G. A. PAGONIS ,99 CONTINUOUS VACUUM AND INERT GAS PROCESS FOR TREATING TITANIUM AND OTHER METALS Filed D80. 31, 1959 5 Sheets-Sheet 4 INVENTOR.

N 6601296 A. Pagazzz's 14 T TORNE Y5 3,116,998 AND INERT GAS PROCESS NIUM AND OTHER METALS B N 0 m P C 4 6 1 7n m FOR TREATING TITA Filed Dec. 31, 1959 5 Sheets-Sheet 5 INVENTOR. $601376 11. Pagans fi z BY J

HTTORNEYS 3,116,998 CONTHJUOUS VACUUM AND INERT GAS PROC- ESS FOR TREATING TITANIUM AND OTHER METALS George A. Pagonis, Santa Clara, Calif., assignor to Light Metals Research Laboratory, Inc., San Jose, Calif. Filed Dec. 31, 1959, Ser. No. 863,329 27 Claims. (Cl. 7545) This invention relates to a novel method for treating, processing and producing metals and alloys by a Continu-ous Vacuum and Inert Gas Process and Apparatus tending to produce metals and alloys of superior physical and mechanical properties of consistent homogeneous uniformity and structural perfection.

This invention is a continuation-in-part of my 'copending applications entitled Process for Treating Titanium and Other Meta-ls, Serial No. 505,887, filed May 4, 1955, now abandoned, and Process and Apparatus for Treating Titanium and Other Metals, Serial No. 775,994, filed November 21, 1958, now Patent No. 3,079,451, granted February 26, 1963.

Research metallurgists and engineers have long realized that metals and alloys processed by conventional methods have many drawbacks often associated with the presence of indefinite quantities of unavoidable contaminants tending to induce countless structural imperfections. The need to transform the melting and alloying procedures to a more exact science has long been recognized by research metallurgists and engineers all over the world. In line with this research, the batch-vacuum method using arc and induction principles, the electno-refining melting methods, the electro-beam and electrodeibombardment melting method and the zone melting and refining method offered definite advantages over the conventional methods. Nevertheless, all these methods are of the batch type and have no provisions to hold a molten pool, and are definitely limited in their application to attain either consistency or homogeneity. present invention will produce metals and super-alloys homogeneously consistent, since the apparatus and process lends itself to such an operation.

The invention is especially adapted to the melting, purifying and alloying of metals which are highly reactive at elevated temperatures, such as titanium, thorium, zirconium, and hafnium, but can be used with advantage with other metals, including magnesium, aluminum, iron and alloys thereof. The invention may be utilized for the recovery of scrap metal as well as for the production of ingots, castings, billets, bars, etc., of pure metal or alloy from sponge metal, and other sources.

One of the primary objects of invention is to provide a process which will improve the physical, mechanical and chemical properties of present-day metals and to produce metals and base alloys having a high degree of purity of greater strength, high ductility and consistent homogeneous uniformity.

Another object of this invention is to provide a novel method for conditioning sponge metal, ingot or scrap, for use in a melting process without necessitating the preprocessing steps of leaching, washing and granulating such metals according to the present-day practices pertaining to methods of melting and alloying the aforesaid metals.

Another object of the invention is to provide a continuous vacuum and inert atmosphere process-apparatus for treating, and producing metals and alloys of high physical and mechanical properties, and at a lower cost.

Another object of the invention is to provide a novel and rapid method for adding neutralizing, scavenging and improver elements and for removing impurities from a body of molten metal while excluding atmospheric con taminants therefrom.

A further object of the invention is the provision of a method for pretreating alloying elements and for int s atent 'ice' 2 trodu'c-ing said alloying elements into a body of molten metal so as to avoid inclusion of impurities and in such manner as to insure homogeneity of the alloying elements in the melt.

A further object of this invention is to provide a novel method for transferring and controlling the flow of molten material between two or more adjacent metal-treating devices.

A still further object of the invention is the treatment of reactive metals in special refractories, the compositions thereof remaining neutral while subjected to elevated temperatures so as to eifect no reaction with the melt.

A further object of the invention is the provision of induction heating of the metals during melting and treatment in such manner as to eliminate the possibility of overheating the crucible liner and in such manner as to increase the speed and penetration of the magnetic field Without effecting skin penetration of the refractory.

Another object of this invention is to provide commercially pure metals and base alloys of consistent and homogeneous composition through the use of an econornical process involving induction heating and continuous application of vacuum and inert gas in novel sequence.

Another object of this invention is to provide a process for producing from titanium scrap metals and other source materials, ingots, billets, castings or test bars having a homogeneous uniformity and grain refinement of such consistency that government agencies, private industries and the national testing associations will be able to certify and register standard specifications for commercially pure titanium and titanium base alloys.

Another object of the invention is to produce titanium metal and titanium base alloys of higher stability and which will better withstand fatigue, stresses and strains at elevated temperatures, thus hastening the application of this metal and its alloys into many more fields.

A further object of the invention is to introduce a new method of processing and stabilizing refractories that will remain neutral and be free from inversion, errosion and thermo-shock for a long period of time, and also will reduce maintenance cost.

A further object of this invention is to produce metals and alloys by an economical method of compactness and continuity, by increasing productivity and reducing power consumption by retaining constant temperatures and thus effecting a great economy.

A further object of this invention is the unique method applied in the purification and the segregation of undesirable elements adversely affecting the physical and mechanical properties of the processed metals, thus making it possible to attain the ultimate in structural perfection and produce superalloys.

Other and further objects and advantages of this invention will become evident from a consideration of the following specification when read in conjunction with the annexed drawings, wherein:

FIG. 1 is an elevational view of metallurgical apparatus for carrying out the process of the invention, including a charging section, melting crucible, purifying crucible, alloying crucible, pouring system and auxiliary equipment;

FIG. 2 is an enlarged fragmentary view, partially in section, illustrating the charging section of the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view, taken substantially on the horizontal plane of line 33 of FIG. 2, looking in the direction of the arrows, and illustrating in greater detail the charging mechanism;

FIG. 4 is a vertical cross-section view taken substantially on the vertical plane of line 44 of FIG. 2, looking in the direction of the arrows, and illustrating pivot FIG. 6is a vertical cross-sectional view of the first or melting crucible, illustrating the component parts thereof in detail as well as of associated equipment pertinent thereto; V FIG. 7 is an' 'enlarg ed vertical fragmentarycross-section'al view of the top OfjllhQSCOIld or purifying crucible employed in this process and illustrating in detailrmeans for pretreating and adding scavengingelements to the crubible and purities}- e I 'Sfis a vertical fragmentarycross-sectional view of the :top of thethird or, alloying crucible, and illustrating the'constructional details ofthe .means. for vpretreating and adding alloying elements'thereto; e FIG. 9 is an. isometric viewof the sampling and transfer valve utilized in they discharge conduits from the crucibles of the apparatus; i e

FIG. 10 is across-sectional view taken on lines 10 10 of,FIG. 9; 1 FIGQII is across-sectional view taken onthe lines 11-11 of FIG. 9;. q I FIG. 12 i s a cross-sectional view taken on the ,lines 12-1 2.of,FIG.-9;' v I, I e

FIG.- 13 is a vertical-sectionalview taken on the lines 1313 of FIG. 7; and y -v- FIG; 14. is an exploded .view in isometric projection showingthe components of a seal-tight-gate valve utilized in the portion of the apparatus shown in FIG. 7.

The process of the invention, as maybe seen from the drawings, particularly FIG. 1, is carriedout in a closed, continuous-system completely sealed fromthe atmosphere and ineach stage of the system the metal is continuously subjected either to vacuum, inert gas or. combinations thereof.- Novel'aspects of the invention are involved in the manner of charging of the system with the metalto be treatedythe preheatingand surface degasifying of the charge and of all additives tokthe charge, the melting for withdrawing, and condensing. volatileflimchamber and its associated comoperation, thepurifying operation, the alloying operation,

the casting operation, thesampling of the metal between stages and the transfer of molten metalxfrom stageto stage. Inert gas is utilized in ,the'melting, purifying and alloying operations-for the-purpose. of excluding atmospheric contaminants,protecting the refractories, and for stirring themelt to insurehomogeneity. In at least one stage ofthe operation, inert gas is introducedvintothe bottom of a relatively deep body of the. molten metal to cause such gas to-permeate the molten metal and: drive the impurities to the surface,-, such impurities being removed from 'said surface byithe simultaneous applica-. tion of a vacuum above such surface.-, Inert. gas ,is also utilized in transferring and sampling operations to proan alloying crucible D, sampling and transferring valves E, and pouring units F. The purifyingcrucible C'has a special top section G for the addition of and pretreatment of scavenging elements and for the removal of volatile impurities. The alloying crucible D has a special topsection H for the'addition of and pretreatment of alloying constituents. Inert gas, such'asfiargonor helium, is supplied from a tank 10, where it is stored under-high pressure,'through anexpansion valve 11', purifier 12, and preheater -14to the base of each crucible, the supply of gas being controlled by valves 15, which are operated automatically or manually in response to pressure indicated by gauges .16. Inert gas is also supplied to the top of each crucible through valved conduits 17. Vacuum may be applied to the top 'of each crucible by means of vacuum line 18 and valves 19, which also are controlled in response to'pressure indicated by gauge 16. Each pouring unit F is also connected to thesourcesof inert gas and vacuum as shown.- i

' THE MFLTING CRUCIBL E The melting crucible B, shown indetail' in FIG. 6, comprises an outer shell including an'elongated, substantially hollow, .cyclindrical side Wall '22 having a'circular base plate 24 and an open end oppositely disposed with respect to the latter. 'The outer shell may be formed of low, carbon steel, aluminum .or copper. The side wall 22 adjacent its upper-end, is formed' with'an aperture 26 for a charging inlet, and below. adjacent the base plate 24, is provided a second aperture 28 for a drain outlet. Substantially diametrically opposed to the drain aperture 28, the side wallv22 has another discharge apertureSt) with the center point of thelatter being higher than the center point-of'the former To' prevent eddy currents and inadvertent or accidental arcing between induction heating means '(to be described below) and the side wall 22sand its associated base plate 24,the wall 22 and base 24, if made of steel, are provided with a thin coating of lead paint (not shown), or may be'provided' with an interior copper'laminate.

lnteriorly 'of'the outer shell and co-extensivewith the sidewall 22 and base plate 24' is a liner'32 formed of asbestos material; Additional insulating layers inwardly from the asbestos liner '32 comprise diatomaceousmaterial34, ahollow tubular'shell-36 of formed alumina, a layer of granulatedalumina 38, a sleeve or shell of mica 40, and a layer of granulated zirconia 42;] Next to 'the granulated zirconia is a molybdenum sheath 44, 'the'u'pper end' of'the'latter'terrninating in a horizontal plane containing a linepassing through the center point of the aperture 26. From that point upwardly is provided 'a substantially cylindrical shell 46 formed of alumina ma-' terial. An inner lining 48' is of a special refractory inaterial, preferably composed of a'mixture of thoria, zirconia,'hafnia, and yttria, constructed and stabilized in a manner to be described in detail below. The molybdenum sheath-Maround the refractory liner'48 has theduel purpose of (1) serving as a heat-conducting medium for vide apressure differential to facilitate rapid flow of the molten metal. Vacuum andinert- .gas are utilized in the pretreatment of thewapparatusduring stabilization of the refractories to flush impurities therefrom. Vacuum is also utilized for the surface degasifying ofthe materials added to the apparatus. In the purifying stage of the operation, the application of a vacuum for drawing ofi volatile impurities is foll wed byv the application of aninert gas pressure above thesurface of the melt to effect rapid settlingof precipitated impurities from such melt. t. s; r, Referring now to the drawings and especially to FIG. 1, the closed' system is shown to comprise acharging section A, a melting crucible B, a purifying crucibleC,

the initial heating of the crucible refractory and 2) as a shield in' case'of refractory failure.

At'the base of the crucible B supported by diatomaceo'usmaterial 34 is a circular disc 52 formed of alumina having an upright, centrally disposed, conically'shaped boss 54 provided with an axial bore 56. "Superimposed over the disc 52 is 'a'second disc 58 constructed of formed alumina and having a dome 60'nesting'or telescoping over-the boss 54. The dome 60' is constructed with a bore 62 coaxiallyaligned'with the bore 56. The lower ends of the alumina shell 36'and granulated alumina 38 are supported on the disc 58 and circumferentially embrace a cover member 64 formed of alumina and having] an upright circumferential flange 66 and a second flange 68"disposed inwardly thereof and con centric therewith.

iiiember 64 is filled with granulated alumina 72. The lower end of the Zirconia layer 42 terminates in a domed, circular base '74 which, in turn, supports domed bottom portion 76 of the molybdenum sheath 44. The special refractory liner 48 is formed with an integral base 78, which is also dome-shaped in configuration.

Imbedded in the cover n4 is a hollow tubular induction heating coil 79 having a beehive configuration, the ends 81) of which are connected with a source of liquid or gaseous coolant under pressure and with a source of high-frequency, alternating current through leads 81.

The crucible B adjacent its upper end, receives through the aperture 26 and through the outermost heat insulators referred to above, a cylindrical conduit 82 formed of titanium or other metal to be treated in the system, which opens at its inner end into the special refractory 48, while the other end thereof abuts against a Zirconia sealing ring 83 supported in the open end of a steel connector sleeve 34. Surrounding the conduit 82 is a sleeve 86 formed of alumina and in which is imbedded a helicoidal electrical resistance element 88 having terminal ends 99 and 2 connected with a source of electricity. The space 94 within the titanium conduit 82 will hereinafter be referred to as the pre-heat chamber. Conduit 82 is perforated around its outer end, as at 965, to permit inert gas to be passed over a charge in preheat chamber 94 from manifold 97 and inlet tube 9%. The electrical resistance element 88 is constructed in such manner as to provide temperatures up to 2000 F. in chamber 94.

To the exterior end of the connector sleeve 84 is joined a valve casing 102 formed of steel and having a gate valve 104 constructed of steel mounted for reciprocation therein and manually operable by wheel 1115. A modified type of valve suitable for use at this point is disclosed in copending application Serial No. 863,289, filed December 31, 1959.

The lower discharge aperture 28 of the steel shell receives therethrough a hollow, cylindrical, open-ended insert 1116 of said special refractory material. The insert extends through the above-mentioned insulating layers and at its inner end opens into melting chamber 1il7 through an opening in the refractory 48. Insert 1% is surrounded by a cylindrical molybdenum sheath 1% and the latter is encircled by a sleeve 111? formed of alumina and having a hollow, tubular, helicoidal induction heating coil 112 imbedded therein and adapted, when desired, to be cooled by passage of water or other liquid or gaseous coolant therethrough. Leads 114 and 116 serve to connect the coil 112 with a suitable source of E.M.F.

An elbow connector 118 is connected to the side wall 22 and has an end thereof physically secured thereto in concentric relation relative to the aperture 28. The elbow connector is provided with an elbow liner 120 formed of alumina, and a substantially hollow, open-ended valve insert 122 formed of the same material is coaxially aligned with the insert 166. As is seen in FIG. 6, the refractory insert 122 joins an arcuately shaped, hollow, tubular refractory liner 124 which is in open communication with the open end of a molten metal discharge tube 126 of special refractory surrounded by a descending section 128 of the liner 120. The latter is, in turn, embraced by a hollow, tubular descending section 130 of the connector 118. The insert 122 contains for reciprocation therethrough a valve-plug 132 formed of said special refractory material and controlled by wheel 134. When the plug 132 is retracted as shown, a continuous discharge passage 135 is provided from the lowermost portion of the melting chamber 1 6:7. The waste or residue discharge passage 135 is used to empty the melting chamber 107 if it becomes necessary. When the plug 132 is closed, the molten metal in the chamber 197 can contact only the special refractory material.

In receiving relation to discharge passage 135 is an ingot mold 136 having an outer shell 138 of metal or other suitable material. The mold 136 is provided with an alumina liner 140 and an inner hollow body 142 formed of stainless steel having a refractory liner 144, which may be formed by spraying the inside of the stainless steel body with said special refractory material. The upper end of the inner body 142 is connected to a cap 146 having an inert gas admission passage 148 formed therein and a passage 150 connected with the vacuum source (FIG. 1). The cap 146 receives the lower end of a valve housing 152 having a gate valve 154 which in closed position extends across the lower end of the tube 126. A heat transfer coil 156 is juxtaposed against the liner 140 for temperature control of the mold. A modified form of mold and valve structure suitable for unit F is disclosed in my copending application Serial No. 843,533, filed September 30, 1959.

Conduits 158, 15E and 16th in the bottom 24 of the outer steel shell of the melting crucible are connected to the source of inert gas under pressure, the conduits communicating with passages 162, 163 and 164 and pores and crevasses in the diatomaceous earth layer 34 for diffusion through the several insulating layers described above and through small openings 166 formed in the molybdenum sheath 44 to serve a function to be described. The inert gas, which eventually finds its way into the top of chamber 107, is exhausted by means of a series of passages 168 at the top of the crucible, such passages being connected through conduits 170 with the suitable vacuum source.

The discharge aperture 30 of the crucible shell has connected thereto an elongated conduit 182 in which is housed an elongated, hollow, tubular, open-ended insert 184 formed of the special refractory material. Surrounding the insert 134 is a sleeve 186 of molybdenum metal which is backed by granulated alumina 188. Around the alumina layer 188 is an induction heating unit comprising a sleeve 190 of formed alumina having a hollow, tubular, helicoidal induction coil 192 embedded therein. The ends 193 of this coil are connected to a source of high-frequency, alternating current by means of electrical contacts 1%. This coil 192, like the other induction heating units, is adapted to receive a cooling liquid or gas. Between the metal conduit 182 and heating unit 1% are insulating materials as disclosed with reference to the melting crucible. The hollow refractory insert 184 provides a passage 1% which connects the melting chamber 1417 of the melting crucible B through the sampling and transfer valve E to the purifying crucible C. The conduit section of the downstream side of the valve E is identical to that just described.

The top of the melting crucible B is closed by means of a cover member 2110 of low-carbon steel, copper or aluminum, which is clamped to the wall 22 in sealed relation therewith by means of a series of bolts 202. Within the cover member is an inner liner 204 of the special refractory material backed by formed alumina 206. A gasket 208 of neoprene-impregnated asbestos material is interposed between the refractory linear 204 and the ends of the various insulating layers of the crucible.

The top of the refractory lining 48 is provided with a circumferential groove 210, covered at its top by the inner portion of gasket 208 to provide a gas manifold for inert gas introduced through a passageway 212 in the insulating layers 204 and 2136 and gasket 268. Passageway 212 communicates with an inert gas supply line 214 by means of a connector 216 in the steel cover 2110. Formed within the refractory liner 48 are a plurality of vertical passageways 218 which have openings 220 near the bottom of the melting chamber 107. The tops of the passageways 218 communicate with the manifold 210 so that inert gas supplied through the line 214 may be introduced into the melt within chamber 197 near the bottom thereof, to permeate and stir such melt.

The cover 2% may contain more than one passage 168 whereby vacuum can be rapidly applied to the chamber 107 above the top of any molten metal therein. Inert gas can also beapplied through the passages 16850 as to increase the pressure'above themelt when desired. An opening 226-is provided through the insulating materials and shell at the apexof the cover,-and' a quartz sight glass 228 is mounted over this 'opening' by means of a flanged sleeve 230 and attached retainer ring 232 so that melting conditions may be observed. 'Pressure gauge 16 permits pressure conditions within the crucible to be determined and regulated. If desired, pressure gauge 16 may be substituted by a pressure recording-controller.

which, through a conventional servo-mechanism (not shown), automatically controls the operation of valves and 19 in'the inert gas and vacuum lines, respectively, these valvesin this instance being of the automatic type. A temperature recording-controller 238 (having conventional control means, not shown, operable on the induction heating-circuit), 'is also mounted on the cover so that the temperature within the crucible'may be exactly set and controlled. a v

THE CHARGING sac non The chargingsection A, as illustrated in detail in FIGS.

2-5,v comprises a double-acting hydraulic cylinder 31%) attachedto a housing 312 for a charging sleeve 314, which provides a charging chamber-.316. The housing 312, in one position as shown in solid lines in FIG. 2, is adapted to be connected insealed relation to a'flange 318 of the valve 1G2 defining the entrance to preheating chamber 94 withinthe walls of the melting crucible A.- An airtight seal between valve flange 318 and housing 312 is effected by meansof an O-ring 322 and quick-acting clamp 324. The housing 312 andhydrauliccylinde'r 310 are mounted upon a carriage 326, which is provided'with rollers 328 receivable within tracks 331) "so that the charging section can be rolledback as a unit-from the melting crucible B when valve'192 is closed and the quick-acting clamp 324 is disengaged.

Track 339 extends'downwardly at its rear portion 332 so that as the carriage 326 moves rearwardly the housing 310 can be tipped up, as shownin dotted lines in FIG. 2. In this position, the chamber 316 is ready to receive acharge'of the metal to be processed. v

The sleeve 314 has a piston ram 334 mounted for movement therein by means of piston rod 336. In the charge-receiving position, the sleeve 314 is retracted with in its housing 312 and the ram'334 is in its fully retracted position. In this positiomthe metal to be processed can be loaded into the sleeve 314' so as to fill or partially fill chamber 316. When the chamber 316 is filled to the desired extent, the entire hydraulic system and housing 312 arebrought forward and locked to the valve flange 318 by means of the quick-acting clamp 324, the O-ring 322 between the flange faces forming a vacuum-type seal between the two sections. l

The sliding valve 1&2 which separates the preheating chamber 94 from the charging mechanism A, is constructed so-that when it is closed a vacuum-tight seal is maintained between the chamber 316 and chamber. 94. The sleeve 314 and piston 334 of the charging mechanism, as well as the liner 82 of the preheating chamber 94, are preferably made of the particular metal to be processed, e.g., titanium, thus avoiding the accidental introduction of other metals by. abrasion of the surfaces contacted by the charge, into the melt during the charging operation. l

A tube 353 connected to inert gas and vacuum lines through valves 352 and 354 'is provided'on the charging side of the valve 162, so as to permit inert gas flushing and vacuum degasifying of the charge in chamber 316 when valve 164' is closed and the housing 812 is clamped to flange 318; p

A modified form of charging mechanism suitable for carrying out the process of this invention is disclosed in copending applications Serial Nos. 505,887 and 775,994,

aforementioned. I

SAMPLING ANDTRANYSFER VALVE encased within a molybdenum sleeve 358. The cylinder 356 contains a valve piston 360 also of said refractory material machined to fit snugly inside the sleeve 356 and adapted to be reciprocated there-in by means of valve stem 362 and wheel 364. The top of the valve is pro vided with a'finned section 365 so that the valve operating mechanism can be prevented from overheating. 'Inert gas inlets 368 and 369 are provided at the top and-bottom ofthe valve housing and a vacuum outlet 370 is also providednear the top ofthe housing. A constant inert gas pressure can be-maintained-within the valve housing to avoid molten metal penetration of the parts.

The valve cylinder and molybdenum sleeve358 are provided with openings 372, which register with the openings in the inner liner of the connected conduit sections. The valve piston sea is provided with a passageway 374 having an opening at one end of the same dirnension as the opening37- in the valve cylinder, and an opening 376 in the other end of reduced dimension. The valve stem 362 is provided with a lever 378 whereby'in the lowermost position of the valve piston 360 the valve stem and piston can be rotated-through a-degree angle. When the valve piston 36% is in its upper position, the passageway 374 is in alignment with the opening 372 in the valve sleeve and can receive molten metal from an adjacent crucible. The filled passageway 3'74 provides a sample slug of molten metal. The piston 360 is then lowered to the position shown in FIG. 10 and the sample slug is allowed to cool. When the sample slug has solidified and cooled to about'1200 B, it is ejected through a (1001' 3'79 into a vacuum chamber 330 by retracting door'screw 332 and advancing an ejector bolt 384. The door 3'79 is then closed, the ejector bolt 384 retracted and the valve piston 36% rotated by means of lever 3'78 so that it can be moved by the action of Wheel 364 on valve stem 362 to 'its upper position for either receiving another sample or for permitting transfer of molten metal from one apparatus unit to the other. The sample slug, indicated at 388, deposited in' the vacuum chamber ass is further cooled while vacuum is applied by means of vacuum line 3% and then removed from this chamber through another sealed door 390 for analysis. This method of sampling molten metals permits a quick analysis to be made of the chemical condition of the melt and enables the attainment of a high degree of uniform consistency control.

Another form of sampling and transfer valve suitable for the purposes of carrying out the process is described in my copending applications Serial Nos. 505,887 and 775,994 and in my Patent No. 2,869,370.

PURIFYING CRUCIBLE The purifying crucible C is constructed in a similar manner to the melting crucible previously described except for the top section G, which is shown in detail in FIG. 7. The capacity of the purifying crucible, however, is preferably about one-half the capacity of the melting crucible, so that the melting crucible retains a substantial body of melt even after molten metal has been withdrawn to fill the purifying crucible. The ingot mold outlet F, transferconduit and sampling and transfer valve 9 system are identical to that just described. Suitable pressure gauges and temperature recording and control means are provided.

The top section G of the purifying crucible C provides a combined condensing and scavenger preheating section. In place of the flanged sleeve 238 at the top of the melting crucible, the purifying crucible C is provided with a valve and condenser housing 488 of low-carbon steel provided with a dome-shaped cover 482, the top of which is connected to a vacuum line 48 Cover 4 92 is held in sealed relation to housing 480 by means of U-bolts 485 and wing nuts 406. Disposed within the bottom portion of the housing 4% is a tubular liner 488 of the special refractory material.

The valve section of this unit is of a special rising-stem gate valve type having sealing and locking means. It comprises top-and bottom steel plates 4N and 412 held in place within the housing 4th) by means of tongues 414 and grooves 416, and by an end plate 4-18. Intermediate the plates 41% and 412 is a split sliding valve element 419 having an upper section 428 and lower section 422. designed to slide together to open-and-closed positions of the valve. A downwardly directed cylindrical projection 423 in the top section which fits in opening 424 in the bottom section prevents longitudinal and lateral shifting of the sections with respect to each other but permits vertical separation. This extension also functions to prevent passage of vapors outwardly between the two valve sections. An opening 4-25 is provided in valve section 429 and projection 423, which in the retracted or open position of the valve as shown in FIG. 7, registers with openings 425 in the plates 4143 and 412. A Wheel 6128 working upon a threaded hollow valve stem 438 is utilized to advance and retract the valve sections. The valve sections 429 and 422 may be spread apart and tightly locked in position against steel plates 41% and 412 by means of cams 432 operated by a shaft 434- within the hollow valve stem and connected to lever 436. Thus, in the closed position of the valve (as shown in FIG. 8, with a similar type of valve used in top section H), the purifying crucible can be tightly sealed by means of the lower section 422 of the valve being forced against its plate while the chamber above the valve is sealed by top section 420 being forced against the upper plate.

The upper portion of the housing 480 contains an outer sleeve 438 which rests upon upper plate 412. At the bottom of this sleeve is placed an annular insert 4 38 upon which a cooling coil 4-42 rests. The cooling coil is spirally wound around the sleeve 438 and is adapted to receive cooling fluid from a source not shown. Within the sleeve 438 is a condenser sleeve M4 upon which volatile impurities from the purifying crucibles are adapted to be condensed during the scavenging operation later described. The top of sleeve 4-44 is attached to a circular disc 446 which is clamped between the housing 488 and cover 402, O-rings 448 being provided at this point to secure a vacuum-tight seal. A screen 45%) covers the top of the sleeve 444 and is held in place by means of bolts 452 which also secure a handle 4-54 to the condenser sleeve assembly. When the cover 482 is removed from the housing 488, the condenser sleeve 444, screen 458 and disc 4-46 are readily removed by a vertically upward pull upon the handle 454.

The top plate 412 is provided with an electrical resistance heating unit 45-5 adapted to be attached to a source of electricity by means of leads 458. When the valve sections are closed, as shown in the analogous structure in FIG. 8, cover 482 may be opened, condenser sleeve unit withdrawn and a cartridge of scavenger elements (shown in dotted lines at 46-5) disposed upon the upper surface of valve section 429. The condenser sleeve and cover are then re-assembled. The cartridge of scavenging elements resting upon the upper valve section 429 is heated by means of coil 456 to a suitable temperature, for example, around 12GO1500 R, while a vacuum is being pulled through line 404. In this manner, scavenging elements are surface-degasified prior to the time they are introduced into the melting and purifying furnace. The cartridge 460 is dropped into the purifying crucible by unlocking and withdrawing the valve to the position shown in FIG. 7. The interior of the housing 400 may be placed under inert gas pressure through valved conduit 462.

The valve structure at the top of the purifying crucible alternatively may be of the structure disclosed in my copending application Serial No. 863,289, filed December 31, 1959, now Patent No. 3,018,789, granted January 30, 1962.

THE ALLOYING CRUCIBLE The alloying crucible D is identical to the purifying crucible C except for the top section H. This top section, as shown in FIG. 8, differs from the top section G of the purifying crucible in that no condenser means need be provided. Thus, a housing 468 is provided which accommodates a split, seal-tight gate valve 470 which is identical to that shown in FIG. 7, except that the top plate does not contain a heating unit. The housing 488 in the top section H is provided with a resistance heating unit 472 which comprises resistance Wire coil 474 embedded in an alumina form. A cover member 476 is provided for the housing 468 and is formed integrally with a section of conduit 478 which provides an alloy preheating and degasifying chamber 480. A cartridge 482 of alloying constituents is shown in place upon the top surface of the sealed gate valve in the chamber 489. A closure member 484 is provided for the top of the conduit 478. This closure member is, in turn, connected to the source of vacuum through flexible vacuum line 486. Closure member 484 may be readily removed by releasing swinging bolts 488 so as to provide access to the chamber 480. It will be understood that suitable gaskets are provided so as to ensure sealing relationship between the various closure members. The interior of the housing 468 may be placed under inert gas pressure through valved conduit 490. The resistance heating element 472 is of such design as to provide temperatures up to l8002000 F. within the alloying chamber 480.

It will be understood that in the operation of the process and apparatus as previously described, suitable auxiliary equipment may include induction units of the motor generator type (rated, for example, at 30 to 50 kw.), additional vacuum pumps, coolant supply lines and pumps, pressure regulating and reduction valves, temperature measuring, control and recording instruments, and analytical equipment necessary for the determination of sample specification.

Each unit of the apparatus is separately controlled as to vacuum, inert gas pressures and temperatures. The process steps, however, in the overall operation are interrelated and cooperate to provide a uniform product with a high degree of accuracy and quality control. The prepurified and preheated inert atmosphere for flushing the apparatus is vacuumed and replenished at regular intervals, and this plus the constant temperatures retained throughout the entire system tends to keep the refractories in a state of stability and neutrality, thereby providing for long life and low maintenance cost.

PROCESSING OF REFRACTORIES One of the problems in producing titanium and other high-melting point metals of uniform consistency has resided in the difficulty in finding a refractory material which will retain a molten pool of the metal without refractory deterioration or metal contamination. T o overcome this problem, the present invention relies on the refractory processing and stabilizing technique previously mentioned and described in detail below. The refractories preferably are prepared from two or more refractory oxides selected from the group consisting of thoria, hafnia, zirconia any yttria. These refractories provide good resistance to tors as described herein are also of importance and constitute inventive features.

A combination of refractory oxides escepially useful in processing molten metals is as follows:

Percent ThO 75 to 95 HfO 6 to 10 ZrO 3 to 7 Y203 1 t 3 A mixture utilizing 85% ThO 8% HfO ZrO and 2% Y O has been found quite satisfactory for titanium processing, and when properly stabilized will have a long life in contact with the molten metals during all processing operations.

The preferred method of preparing the special refractory oxide liner is as follows:

A fused calcined mixture of ThO HfO ZrO and Y O in the proportions given above is crushed in an earth or granite mortar to form a grog which will pass through a 325-mesh screen. All contact with metals during the grinding operation is avoided so as to prevent contamination of the calcine. The finely ground oxides are then mixed with about 10% of polyethylene glycol and a bonding material such as stearic acid. This mixture is then partially dried and aerated while being rubbed through a 14-mesh screen, and it is then ready for pressing. A welded sheath of formed molybdenum is placed in a steel mold, the mixed refractories are then rammed into the mold uniformly with a molybdenum-sheathed ram, and are further compressed hydraulically to about 32,000 p.s.i. to form a strong crucible liner. These crucibles and their sheaths are placed in a vacuum oven and heated to about 800 F. under a vacum on the order .of about 10 mm. Hg for about eight hours and are allowed to cool to room temperatures in the oven under vacuum. All of the other special refractories utilized in the apparatus that come in contact with the molten titanium or other metal to be processed are treated in the same manner. 7

After the special refractory linings have been assembled in the apparatus as previously disclosed, the sliding valve elements of the sampling and transfer valves E are opened to ensure communication of crucibles B, C and D. The valves to the ingot molds F and to top sections G and H are also opened, as well as the valve 102 to the charging section, this section being clamped to the preheat section. All other valves are closed so as to seal the entire system from the atmosphere. The induction heating elements are then energized in the entire system, while a vacuum of 10 mm. Hg is drawn through the various communications to the vacuum line, all valves to the vacuum being opened.

During the first stage of heating, the temperature of the entire system is increased uniformly to 1200 F. in a period of eight hours. At this stage, the refractories are conductive. The speed of evacuating is then reduced, and purified, preheated, and pre-expanded inert gas is introduced throughout the system by means of the various communuications to the inert gas source. The inert gas may be heated to 800-1200 P. All gate valves are now gradually closed, sealing the individual stages from each other. The vacuum to the ingot molds, charging section and preheat sections G and H is cut off and these units are maintained under inert gas pressure while the crucible refractories are further stabilized. The valves 15 supplying inert gas to the bottom of the crucibles and the valves 19 12 to the vacuum line at the top of the crucibles are pressureregulated to function as follows:

When the inert atmosphere pressure has reached approximately 12 pounds gauge pressure, the vacuum valves 19 are opened and the inert gas valves 15 are shut off. The procedure is reversed when the inert gas pressure has dropped to about three pounds gauge. VJith this procedure, the entire refractory system of the crucibles is continuously flushed with pre-purified inert gas, thus keeping a pure atmosphere throughout.

The second stage of heating is set for 2500 F. for the next eight hours while the flushing and evacuating procedures are repeated at regular intervals. In the third stage of stabilization, the refractories of the crucibles are uniformly heated to 3270 F. and held at such temperature for a period of eight hours. It Will thus be seen that a time period of 24 hours is required to completely stabilize the refractories under the constant cycling of inert gas between high and low pressures as has been described above. At this point, the temperature in the melting crucible B is regulated so as to remain at about 3270 F. (slightly above the melting point of commercial titanium heretofore available), while the purifying and alloying furnace crucible temperatures are slightly reduced, to about 3l0O F, or just above the solidifying point of pure titanium as produced in the present process. From this point on, the temperature remains constant while the processing of the titanium begins.

t will be understood that where other metals than titanium are utilized, the same general stabilization procedures would be utilized, but the final temperatures would be adjusted, depending upon the melting point of the particular metal involved, the temperature of the crucibles being maintained slightly above the melting point of such metal.

PRINCIPLES OF OPERATION In describing the operation of the continuous vacuum and inert gas process, the description will relate to five main steps, namely (1) charging and preheating, (2) melting, (3) purifying, (4) alloying, and (5) pouring.

Although this process lends itself for the treatment of all the conventional metals, it can be used with special advantage for the reactive metals (refractory metals) with the same degree of improvement in quality and consistent homogeneity. Titanium will be used to describe the operation of the process and apparatus.

Charging operation.With the vacuum and inert .gas valves 352 and 354 in the closed position and the gate valve 102 separating the preheating chamber 94 from the charging chamber 316 completely closed and sealed, the charging section housing 312 is drawn back to the position shown in dot-dash lines in FIG. 2 and fine titanium scraps or small pieces of titanium sponge are loaded into the cylinder 314. The housing 312 is then closed against the flange of the preheating chamber and locked tightly by clamp 324. The vacuum of the charging section is turned on by opening valve 354. The vacuum applied may range from 10 to 10* mm. Hg. The charge may further be completely flushed of atmos pheric contaminants by alternatively admitting inert gas and then applying vacuum by manipulation of valves 352 and 354.

The gate valve 102 is then opened and the charged titanium placed in the preheating chamber 94 by the hydraulic system, the cylinder 314 and ram 334 being advanced together into the chamber 94, also as shown in dot-dash lines in FIG. 2, and the cylinder 314 then being retracted hydraulically while the ram remains stationary to thereby deposit the charge gently in preheat chamber 94 without contact with the elements of valve 102. After the cylinder 314 and piston ram 334 have returned to their original position, the gate valve 102 is closed and the material preheated in chamber 4 by the resistance coil 8% to about 1900 F. or 2000 F. During the operation inert gas is admitted cyclically to chamber 94- through line 93 while vacuum is drawn at the top of crucible B through line 170 and valve 19. In the presence of the controlled atmosphere, at these temperatures the charged titanium is surlace degasified. A repeated operation follows, and the first charge is injected into the melting crucible. Thus, by repeating the charging, the molten titanium in the crucible reaches its full capacity while the inert gas and the vacuum valves are manipulated to provide cycling between a high of 12 to p.s.i.g. and a low of 2 to 3 p.s.i.g. as has previously been described, thereby flushing the apparatus and materials and removing flushing gases.

Melting.The charging is then stopped momentarily and the molten titanium is prepared for sampling. During the melting operation, in which crucible B is heated to about 3270" F., the molten titanium is permeated with inert gas which, for example, may be argon or helium, this inert gas having been prepurified, preheated and preexpanded, as has been described previously. The inert gas used in the permeation is introduced through openings 226 in the crucible at a pressure causing permeation through the melt, thereby causing the release of gas contaminants which are brought to the surface of the melt and exhausted by the vacuum.

A sample of molten titanium is taken by the sampling and transfer valve E in the form of a cylindrical slug by the following application: The flow of inert gas permeating through the melt is completely stopped by closing the valve in line 214. The inert gas valve located in line 179 in the cover and directly over the melt is now opened (vacuum valve 19 being closed), creating a continuous increase in pressure in melting crucible B while the purifying chamber pressure is now reduced to two-pound gauge by appropriate valve manipulation.

The sampling valve piston 360 is now rotated and raised to the sampling position, shown in dot-dash lines in FIG. 6, so that a minute break-through is noticed from crucible B to crucible C relieving conduit pressure. The molten metal will fully occupy the cylindrical sample space to form the sample slug with substantially no transfer of molten metal to crucible C. The piston 360 is lowered carrying the slug, while the passage between the crucibles is now fully closed.

After the sample slug has solidified and cooled oiT to about 1800 F. while in an atmosphere of inert gas admitted through line 369, it is ejected into the vacuum chamber 380, as previously described. It is then further cooled while subjected to vacuum and then removed and analyzed. Then the valve piston 360 is raised to the transferring posi ion, the opening 376 in this case being in full alignment with the conduit opening to the purifying crucible.

Pressure (e.g., 12 p.s.i.g.) applied from the melting chamber expedites the transferring of the melt into the purifying chamber which may be at about 2 p.s.i.g., as previously indicated, while a rapid analysis is made of the slug to determine the chemical composition of the metal to be purified. When this is accomplished, the appropriate scavenger elements in proper quantities are placed in a titanium cartridge and made ready to be placed in the scavenger chamber, shown in FIG. 7 and previously described. Only a part of the molten titanium is transferred, but its quantity is controlled by filling crucible C to a predetermined height as checked by sight glass or other appropriate means. The volume at this height has been predetermined. Since the melting chamber capacity is twice the capacity of the purifying chamher and only part of the molten titanium is transferred, all charges introduced in the melting chamber fall into a molten titanium bath, which highly expedites the melting and protects the bottom of the crucible from damage by impact.

Purifying.The cartridge (FIG. 7) carrying the scavenger elements is placed in the chamber above the melt, the sliding valve 419 holding the cartridge while the resistance coil 456 heats the cartridge and the vacuum drawn through line 4494 evacuates the scavenger chamber. The cartridge is heated to about 1100 F. while the vacuum is in the order of 10 mm. Hg, accomplishing degasification of the scavenger elements. At these temperatures, the scavenger cartridge 4% is released into the melt by pulling back the sliding valve 419 while inert gas introduced through openings 220 in crucible C agitates the melt and increases pressure.

The drop of the cartridge and the releasing of the scavenging elements in the melt cause an exothermic reaction, producing further agitation and a temporary, slight increase in temperature in the melt, the crucible temperature being approximately 3100 F. While the titanium cartridge is consumed in the melt, the remaining contaminants combine with the scavenger-sublimating elements picked up by the vacuum drawn through line 404 and are directed through the condensing sleeve 444- Where the sublimating vapor elements solidify on the condenser sleeve, which is cooled by passage of cooling fluid through coil 442. The gas contaminants are exhausted into the atmosphere by the vacuum. The following conditions preferably are kept in equilibrium during the purifying and sublimating period:

(1) Pressure of exhaust (vacuum speeds) sufiicient to lower the pressure above the melt to 2 or 3 p.s.i.g.

(2) Pressure of permeation (inert gas) sufficient to agitate melt and permeate all portions thereofabout 12 to 13 p.s.i.g. at line 214.

(3) Temperature of purifying chamber close to but slightly above the solidifying temperature of the molten titanium at all timesapproximately 3100 F. or slightly higher in the initial step.

(4) Speed of sublimating vapor (controlled by composition used in the scavenging elements), sutlicient to complete the sublimation within a period of a few minutes.

(5) Temperature of condensing sleeves below the solidification point of the volatile metallic impurities usually in the order of 1000 F.

The preferred scavenger elements for titanium, which depend on the analysis of the sample and predetermination of the type and quantity of the contaminants present, are listed below. In all cases, the scavenging elements are placed in a titanium cartridge when titanium is the material to be treated and, in all cases, it has been found that the quantity of the scavenger elements need not exceed about 20% of the total volume of all contaminants.

Lithium-silicon alloy Magnesium-cerium alloy Metallic calcium Potassium permanganate (minute quantity, and only when carbon is present, e.g., for each volume of carbon about 1 to 10% by volume of potassium permanganate may be used) The lithium-silicon alloy may contain equal parts by weight of Li and Si, and the magnesium-cerium alloy may comprise pure Mg as a base and 5% Ce. The metallic calcium and potassium permanganate are utilized as such. While these are the preferred materials for scavenging titanium in accordance with the invention and provide the desired rate of sublimation, it will be understood that other scavenging elements, alloys and combinations may be utilized following the general principles of the invention to provide a higher order of purification than has heretofore been possible. Thus, lithium and magnesium may be utilized without alloying, or different alloying proportions can be used. Conventional scavenging materials known to the art for combination with oxygen, nitrogen and other contaminating agents may also be utilized. Further, where the process is used for purification of metals other than titanium, it

is understood that the scavenging agents appropriate'for such other metals would be selected. Thus, in the purification, of some of the conventional metals, small quantities of titanium or Zirconium may be used as scavenging elements. 7 1

The scavenging elements utilized'should, of course, be in the purest form practicable, and suchelements are utilized in powdered or granulated condition, confined within a cartridge. The use of such a cartridge permits the scavenging elements to be carried downwardly through the'mass of molten metal to the bottom thereof of the melt, so'that as the cartridge is consumed .the scavenging elements arer'eleased under the melt and will then permeate the entire mass of molten metal as they volatilize, combining with or entraining carbon, nitrogen and oxygen and carrying'thesecontaminants from the surface of'the melt assisted by the combined action of the gas permeating through the melt' and the'evacution of the gases and vaporsfrom the'ltop of the melting chamber.

The sliding valve 419, which separates the condensing chamber from the purifying crucible, is' closed and sealed immediately after the scavenging reaction ceases, ,thus completely shutting off the vacuumg" Also, the'perr neating inert gas in the crucible is shut off'and the inert gas valve to. line 170 is opened. The inert'gas admitted directly over the molten pool is permitted to build up a pressure over the surface of the melt in the range of 10 to 15 p.s.i.g., the'exact pressure Within this range depending on the quantity of residual elements in the meltthe greater the quantity of residual elements, the higher the pressure. The 'inert' gas surrounding the crucible also is increased to the same value through lines 158, .159 and 160, establishing a state of pressure equilibrium within the purification crucible. i l

At this point, all residual elements or alloying elements that are heavier than titanium and'are grain-suspended in the molten pool are segregated and rest at the bottom of the crucible. These. residual elements maybe flushed out into the Waste ingot mold immediately, or flushedout after the purified molten titanium has been first transferred into the alloying chamber. A time period of one to two minutes at equilibrium is generally sufficient to effect the segregation and settling of the residual elements. Although in specific examples described herein, mention is made only of titanium, aluminum and magnesium, this method of differential pressure application over other metals in their molten state in the same manner Will cause all residual contaminant elements to definitely segregate and rest at the bottom of the crucible, thus efie'ctin'g a total purification of the melt. 7

The sampling of the purified melt is carried on in the same manner as has been described in a previous paragraph in the melting section. If the degree of puri fication is satisfactory, the pure molten metal is then Withdrawn as such into an ingot mold, or is transferred to the alloying crucible D by the previously described transfer technique.

Allying.-'When the analysis of'the titanium is completed and mloying is desired, the alloyingelements selected are then placed in a titanium cartridge and lowered into the alloying preheating chamber 480 of section H (FIGS. 1 and 8) where resistance coils 474 preheat them to about 1800" -F. to 2000 F, depending on the alloying elements selected, in the presence of a vacuum of the order of about10 to 10- mm. Hg drawnthrough line486. At these temperaturessurface contamination of the alloys is totally reduced. Then the [sliding gate. valve element sealing the chamber 480 from they crucible chamber andholding the alloying cartridge 482 is opened momentarily, allowing the cartridge to drop into the molten titanium pool where the permeating inert gas introduced through openings 220 agitatesthe melt.

The temperature'of the molten pool is gradually raised to about 3450" F. to accomplish a superheating effect.

At this point a minute quantity of sulphur dioxide (S0 is introduced into the inert gas, the amount being regulated to'the desired grain refinement and may, for example, constitute one or lWQ p'erce nfo'f' the'permeating gas. Thus, av homogeneous, refined grain alloy is developed. The pressure over the meltin alloying cruci'hle'D is maintained in the order of 3 p.s.i.g. by evacuation of the permeating gases through line '1'70 'at the top of the crucible.

Soon after the titanium alloy has become homogeneous, Which may require several minutes at the superheat temperature, the inert gas is stopped by shutting the valves and'vacuu m is continued through line 107,'thereby reducing inert gas pressure over theunelt to about 2'-po und gauge. The melt is then transferred to the preheated, prevacuumed and prefiushed ingot mold. Alloys made by this process apparatus are consistently exact and accurate'in chemical composition. If desired, crucible D may vbe used for grain-refining pure titanium rather than for' alloying;- a

P0zrring.The moltentitanium or titanium alloy can be poured directly into an ingot mold, electrode bar mold, or into a'bille t mold. In all cases't'ne interior face of the mold is heavily'sprayed with a fine refractory material similar to the spe'cialrefractory lining used 'fo'r the' crucible. The molds are preheated to about 1000' F4, prevacuumed and flushed withinert gas, the pressure of which is held constant at about 12-pound gauge while the molten metal is poured. As soon as about one-fourth of the melt is transferred into the moldfcooling air is circulated through the coil 156 of the mold PIGJ6), bringing about uniform solidification of the form. The molds attached to the melting and purifying furnaces WOl'k' exactly'the'same as the alloy'ingot mold and are used to empty residual materials, to withdraw pure titanium from crucible C, or to emptythe moltenmetal' in case of an emergency in any one of the chambers The advantages of the process are furtherillustrated by the following examples of practice:

Example 1 The process described above was utilized to'provide a pure titanium metal from comrnercial titanium metal. Analysis of the commercial titanium disclosed small quantities of nitrogen, oxygen and iron contaminants, calcu lated to be about 2% by volume of the melt. The scavenging elements were selected as'follows: lithium-silicon alloy (50% Li and 50% Si) 0.02%, magnesium-cerium alloy Mg and 5% Ce) 0.10%, metallic calcium 0.006%, all percentages being based on the total weight of the'melt to be purified. The totalvolumeof the scavenging-in redientsrepresented about 20% by volume or the total estimated contaminating materials. These ingredients were utilized in granular formand were contained Within a titanium cartridge. The improvement in product quality is illustrated by the following compariso Unbleachedsponge titanium was purified in the same manner as described in Example 1; This material by analysis showed the presence of carbon as well as oxygen, nitrogen and iron as contaminants; In addition tot-he scavenging materials used in Example 1, approximately 0.002% of potassium permanganate, based on the total weight of the melt, was used in the scavenging cartridge. The product quality is illustrated by'the following:

TABLE II (a) Sponge, test-bar-cast before processing:

Ultimate strength, average p.s.i 73,800 Yield strength, 0.2% ofiset p.s.i 61,200 Elongation in 2.0 inches percent 18.0 (b) Sponge, test-bar-cast after processing:

Ultimate strength, uniform p.s.i 97,800 Yield stren th, 0.2% olfset p.s.i 77,500 Elongation in 2.0 inches percent 22.0

Example 3 Several titanium alloy scrap metals were processed in the same manner as described in Example 2, utilizing the same scavenging materials. Comparison of the metals before and after processing is as follows:

TABLE III (a) Alloyed titanium SCl'fip before processing:

The alloyed titanium scrap of Table 1H initially contained 0.30%, C, 0.08% N, 0.110% oxygen, and 0.10% Fe as undesirable contaminmts, the alloying constituents being 2.13% Mo, 2.10 Fe, and 2.06% Cr. The alloyed titanium scrap of Table IV initially contained 0.25% C, 0.005% N, 0.09% H, 0.08% oxygen, and 0.06% Fe as undesired contaminants, and 3.05% Mo, 2.08% Fe, 2.06% Cr as alloying constituents. The processing in both instances substantially removed the undesired contaminants.

Example 4 A commercial sand-cast aluminum alloy, identified bel W as an AAX alloy (7.5% Si, 0.4% Mg, total mar' mum impurities of Fe, Mn, Zn and Ti not exceeding 0.5% per volume), was reprocessed by the method described above for titanium, with two specific differences: (1) The temperatures of the melting, purifying and alloying crucibles were gradually reduced to about 1260 F., just above melting temperature for the specific alloy, and the preheating of the charge was reduced to 600 F.; and (2) the scavenger elements utilized comprised a small quantity of titanium powder mixed with a minute quantity of boric acid and the scavenging cartridge (in this case made of aluminum alloy), was preheated to 400 F. N additional alloying elements were added to the purified metal. The inert atmosphere was helium. The product comparison is as follows:

TABLE V (a) AAX before processing:

Tensile strength, average p.s.i 41,000 Yield strength, 0.2% oifset p.s.i 40,000 Elongation in 2.0 inches percent 5.0 (b) AAX after processing:

Tensile strength, uniform p.s.i 52,300 Yield strength 0.2% oiiset p.s.i 51,100 Elongation in 2.0 inches percent 3.0

Example 5 Another commercial sand-cast aluminum alloy, identified as ABX (1.5% Cu, 5.5% Si, 0.6% Mg, total maxiraces mum impurities of Fe, Mn and Zn not exceeding 0.5% per volume), was reprocessed by the same procedure as in Example 4. The product comparison is as follows:

TABLE VI (a) ABX before processing:

Tensile strength, average p.s.i 39,000 Yield strength, 0.2% offset p.s.i 35,000 Elongation in 2.0 inches percent 1.0 (b) ABX after processing:

Tensile strength, uniform p.S.i.. 51,000 Yield strength, 0.2% offset p.s.i 46,400 Elongation in 2.0 inches percent 1.8

Example 6 A commercial sand-cast magnesium alloy, identified as MgX, was reprocessed by the process of the present intion utilizing crucible temperatures of about 1260 F, a charge preheating temperature of about 600 F., and a scavenger preheating temperature of about 400 F. The inert atmosphere applied during the purifying stage was helium, to which a small quantity of S0 had been added. The scavenger elements were lithium and sulp-hur flower sealed in a magnesium alloy cartridge. No additional alloying constituents were added. The product comparison is as follows: i

TABLE VII ((1) MgX Temper F (as cast), before processing:

Tensile strength, average p.s.i 20,000 Yield strength, 0.2% offset p.s.i. 10,000 Elongation in 2.0 inches percent (b) MgX Temper F (as cast), after processing:

Tensile strength, uniform p.s.i. 34,000 Yield strength, 0.2% offset p.s.i 18,000 Elongation in 2.0 inches percent 2.4

Laboratory stress-rupture tests of magnesium and aluminum alloys at temperatures up to 600 F. showed the following advantages of this process over other methods. The following alloys were tested:

A-Mlagnesium sand-cast alloy MgX taken at standard Temper-T6.

B-Al-loy MgX after reprocessing by present process taken at standard Temper-T6. C-Aluminum sand-cast alloy ABX taken at standard Temper-T2.

D-All0y ABX after reprocessing by present process taken at standard Temper-T2.

While it would be possible to conduct an entire purifying, melting and alloying operation in a single crucible of the type described, it is highly preferable from the standpoint of product purity and homogeneity, prolonging the life of the apparatus and providing maximum output capacity to utilize the three-stage apparatus described. Thus, the process is operated in a continuous manner with melting, purification and alloying or refining being conducted substantially simultaneously in the different zones. The first crucible is recharged while purification is proceeding in the second, and the second crucible is replenished while alloying or refining 11S proceeding in the third. No contaminants or undesired constituents are 19 carried over from one stage to the other, since the stages are conducted in separate, isolated zones. No batch operation has yet achieved the product homogeneity and consistency afforded by the continuous process operated in the manner disclosed.

The maintaining of constant temperatures and the introduction of preheated materials into a molten pool highly increases the production capacity, thus effecting a saving in power consumption. For example, a 50-pound capacity unit operating continuously for 30 days can easily produce about 75,000 pounds of titanium, a feat that cannot be duplicated by any type of apparatus twice its capacity. Furthermore, since this is a compact multi-stage process, its cost of manpower operation is greatly reduced. It is evident that titanium and other metals processed by this method will attain higher physical and mechanical properties with more consistency and homogeneity than can be realized by Other methods.

During the entire operation previously described, the crucible refractories are maintained at substantially constant temperature and are flooded with inert gas admitted directly thereto through the bottom of the crucible shell. The pressure of the inert gas so admitted is preferably regulated so as to equalize the gas pressures in the refractories with the pressures within the chambers enclosed by such refmactories. It will be seen that this use of inert gas not only prevents contamination from possible leaks to the atmosphere, but pnolongs the refractory life.

Vacuum for complete evacuation, designated in the drawings (FIG. 1) as high vacuum and in the order of lO tolfi mm. Hg, is applied in the first stage of stabilizing the refractories and thereafter is applied only in the charging chamber A, the scavenger chamber G, the alloying chamber H, the sampling chambers and ingot molds. In the crucibles B, C and D, the pressure varies constantly from a high of about 1215 p.s.i.g. to a low of about 1-3 p.s.i.g., except in the purifying crucible C during the settling of residual impurities. The vacuum applied to the crucibles through the line 170 is merely for the purpose of purging the crucibles at intervals, thereby providing the pressure reduction to 23 p.s.i.g. The specified high and low pressures are not sharply critical but may be varied as desired, provided a cyclic purging and constant inert gas pressure is maintained.

It will be understood that the foregoing exemplifications of the process are by way of illustration and that the invention is limited only by the scope of the appended claims. In the claims, the word metal is also intended to include alloys.

1 claim: 7

1. In a process for improving the physical and chemical properties of a metal, the steps comprising: maintaining said metal in a closed system in contact with an inert gas under pressure above that of the atmosphere throughout a plurality of treating stages during which said metal is converted to molten condition, treated and then solidified, and in at least One of said stages introducing solid scavenging agents into a relatively deep body of said molten metal, introducing inert gas at the bottom of said body of molten metal to drive impurities upward through said melt and from the surface thereof while Withdrawing said impurities from an enclosed space above such surface, and then applying an increased superatmospheric inert gas pressure above the surface of the body of the molten metal to settle out additional impurities.

2. The process as defined in claim 1, comprising the preliminary steps of surface-degasifying the metal to be treated by application of a vacuum thereto prior to melting said metal, introducing said surface-degasified solid metal to a preheating zone of the closed system without contact with the atmosphere, preheating said metal to a temperature below melting while flushing it with inert gas and introducing said preheated metal while in contact with inert gas into a body of molten metal maintained in a melting zone of said closed system.

3. The process as defined in claim 1, comprising the steps of confining said body of molten metal in refractory material flushed with said inert gas.

4. The process of claim 1 wherein the scavenging elements are preheated and surface-degasified under vacuum and are then introduced into the body of the melt without contact with the atmosphere.

5. The process of claim 1 wherein said scavenging elements are encased in a container of the metal being treated and said container is dropped to the bottom of the melt.

6. The process of claim 1 wherein scavenged impurities are sublimed and are condensed by withdrawal through a temperature-controlled sleeve spaced from the surface of the melt.

7. The process of claim 1 comprising the step of introdueing alloying metal into the body of the melt in one of the stages followed by the introduction of said inert gas through the body of the melt to agitate said melt and insure homogeneity of resulting alloy.

8. The process of claim 7 wherein said alloying metal is preheated and surface-degasified under vacuum and is then introduced into the body of the melt without corn tact with the atmosphere.

9. The process of claim 1 wherein said metal is se lected from the group consisting of titanium, thorium, zirconium, hafnium, magnesium, aluminum and iron.

10. In a process for purifying a metal, the steps comprising: confining a relatively deep body of said metal in molten form at a temperature slightly above its melting point in a zone closed from the atmosphere under inert gas at a pressure above atmospheric, introducing solid scavenging agents into: said body of molten metal, introducing inert gas into said body of molten metal near the bottom thereof to permeate and agitate said melt while withdrawing gases from the space above said melt, then discontinuing the introduction of said inert gas at the bottom of said melt and rapidly increasing the inert gas pressure above' said melt to thereby cause said melt to become quiescent and impurities to settle to the bottom thereof.

11. The process of claim 10' wherein said body of molten metal is confined within refractory materials and an inert gas is applied to said refractory materials to equalize the inert gas pressure around and above said body of molten metal during said quiescent period.

12. A process for purifying a metal comprising main taining said metal in continuous contact with inert gas: above atmospheric pressure while passing said metal through a plurality of zones in a closed system, said Zones being capable of isolation from each other; maintaining a relatively deep body of molten metal in each of said zones during the treatment of said metal therein; intermit tently feeding charges of vacuum-surface-degasified, preheated solid metal to the first of said zones into the body of melt maintained therein; transferring portions of molten metal under inert gas pressure from zone to zone, said zones being isolated from one another during treatment of the metal therein, withdrawing portions of the treated metal from the last of said zones; and treating said molten metal in at least one of said zones by introducing inert gas into said body of molten metal near the bottom thereof to permeate the melt and drive off gaseous impurities.

13. The process as defined in claim 12 wherein in the first of said treating zones the metal is partially purified by introducing inert gas through said body of molten metal and withdrawing gases above the surface of the molten metal, and in a subsequent zone scavenging elements are introduced into a body of the molten metal while intro-- ducing inert gas through the melt to drive off scavenged impurities from the surface of the melt.

14. The process of claim 13 wherein the purified molten metal is transferred to an alloying zone of said closed systern, alloying elements are introduced therein and the melt is agitated by the introduction of an inert gas near the bottom thereof to obtain homogeneity of the alloying constituents.

15. The process as defined in claim 12 wherein said zones comprise successive melting, purifying and alloying zones and the molten metal is transferred from adjacent the bottom of one zone to the top of the next successive zone while inent gas pressure is maintained above the surface of the melt in the zone from which said melt is being transferred and a lower inert gas pressure is maintained in the successive zone to which the melt is being transferred.

16. The process as defined in claim 12 wherein the molten metal from the last of said zones is transferred under mert gas pressure to a refractory-lined, preheated, prevacuumed and inert gas-flushed mold and is subjected to controlled cooling therein.

:17. The process of claim 12 wherein the metal is tium, the charges of metal fed to the first zone are preheated to a temperature of about 1900 to 2000" F. While flushed with inert gas, the temperature in the first zone is maintained slightly above the melting point of titanium, and the temperature in the subsequent purifying zone is lower than in the melting zone but is sufficient to keep the titanium in molten form under the conditions therein.

18. In process for the melting and purification of a metal in a closed system, the improvement, comprising: introducing repeated charges of solid metal into a body of molten metal in an induction heating zone of the closed system While maintaining the system at all times under an inert gas pressure above atmospheric, and melting said charges of metal in said zone while subjecting said metal to a cyclic increase and decrease in the inert gas pressure, the cyclic gas pressures being applied by introducing said inert gas into the lower portion of the molten metal in said zone until the inent gas pressure in said zone builds up to a certain maximum value, then discontinuing the introduction of inert gas through the melt and withdrawing inert gas from said zone above the surface of the melt until the inert gas pressure in the zone has dropped to a certain minimum value, and cyclically repeating the introduction and withdrawal of inert gas.

19. A process for improving the properties of titanium comprising, subjecting a charge of titanium to a vacuum to effect surfacesdegasification, preheating said surfacedegasified charge to a temperature below the melting point while flushing it with inert gas, melting said preheated charge while maintaining it under an inert gas pressure above atmospheric pressure and permeating the melt with inert gas introduced near the bottom of a relatively deep body of said melt, withdrawing gases from a closed space above the body of melt, introducing solid scavenging elements i to a relatively deep body of the resulting molten titanium and introducing additional inert gas near the bot-torn of the body of molten titanium while Withdrawscaven ed impurities from the space above the surface of the molten titanium, ceasing the flow of inert gas in then subjecting said body of titanium to an increased superatmospheric inert gas pressure above the surface eof so th t the molten bath becomes quiescent and adional impurities settle out, and pouring and solidifying said purified titanium while it is continuously in contact with inert gas, the titanium being maintained under inert gas pressure above atmospheric pressure at all stages from the preheating to solidifying.

20. The process of claim 19 wherein the scavenging elements are enclosed in a cartridge of titanium, said cartridge is preheated and vacuum-degasified, and is then dropped to the bottom or said molten bath of titanium without contact with the atmosphere.

21. The process of claim 19 wherein an alloying metal is added to the molten and purified titanium before pouring and solidifying.

22. The pro-Jess of claim 21 wherein said alloying metal is preheated and \iacuum-degasified and is dropped into the body of molten titanium without contact with the atmosphere, and the body of molten titanium is super- 2 heated and stirred by introduction of inert gas near the bottom thereof so as to insure alloy homogeneity.

23. A process for treating titanium, comprising: subjecting said titanium to the continuous action of inert gas and vacuum While passing said metal through a plurality of preheated, prevacuurned, inert gas-flushed zones of a closed system, said zones being capable of isolation from each other; maintaining a relatively deep body of molten titanium in each of said zones during treatment of said titanium therein and maintaining said zones under inert gas pressure above atmospheric pressure; feeding charges of preheated, vacuum-sunface-degasified titanium to the first of said zones into the body of molten titanium main tained therein and melting said charges while inert gas is introduced into the molten body of titanium near the bottom thereof and gases are withdrawn from the closed space above the surface of said body; transferring a portion of molten titanium from said first zone to the second zone while maintaining it in contact with inert gas; introducing preheated, prevacuumed scavenging elements into the body of molten titanium in said second zone and permeating said molten body or" titanium with inert gas introduced near the bottom thereof while withdrawing scavenged impurities fnom the space above said molten body, ceasing the introduction of inert gas into the molten titanium in the second zone after the scavenging reaction is complete, applying an increased superatmospheric inert gas pressure above said surface to cause the body of molten titanium to become quiescent and any additional impurities to settle; then transferring the purified titanium from the second to a subsequent zone under inert gas pressure for further treatment or casting, and repeating the purifying operation on further charges from the first zone.

24. The process of claim 23 wherein the molten titanium fnom the second zone is transferred to an alloying zone, preheated vacuum-degasified alloying elements are added to the molten titanium in the alloying zone, the molten metal is superheated and stirred by inert gas in said zone and is then cast under an atmosphere of inert gas.

25. The process of claim 12 wherein a sample of molten metal from a treating zone is withdrawn under inert gas and cooled and solidified out of contact with the atmosphere prior to transfer of molten metal from such zone.

26. A process for improving the properties of a metal, comprising: subjecting a charge of said metal in solid form to a vacuum to effect surface degasificati on, preheating said surface-degasified charge to a temperature below the melting point while flushing it with inert gas, melting said preheated charge while maintaining it under an inent gas pressure above atmospheric pressure and permeating the melt with inert gas introduced near the bottom of a relatively deep body of said melt, withdrawing gases from a closed space above the body of melt, intnoducing solid scavenging elements into a relatively deep body of the resulting molten metal and introducing additional inert gas near the bottom of the body of said molten metal while withdrawing scavenged impurities from the space above the surface of the molten metal, ceasing the llow of inert gas and then subjecting said body of molten metal to an increased superatmospheric gas pressure above the surface thereof so that the molten bath becomes quiescent and additional impurities settle out, and pouring and solidifying said purified metal while it is continuously in contact with inert gas, the metal being maintained under inert gas pressure above atmospheric pressure at all stages from preheating to solidifying.

27. The process of claim 26 wherein said metal is selected from the group consisting of titanium, thorium, zir conium, hafnium, magnesium, aluminum and iron.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Lindenthal Dec. 22, 1891 Surnrney Nov. 10, 1936 Burkhardt Sept. 2, 1947 Kroll Apr. 17, 1951 Tour May 1, 1951 Maddex Aug. 14, 1951 Nisbet Aug. 14, 1951 Urban July 20, 1954 OTHER REFERENCES Crockett: Metal Progress, December 1948, pp. 833836. 

12. A PROCESS FOR PURIFYING A METAL COMPRISING MAINTAINING SAID METAL IN CONTINUOUS CONTACT WITH INERT GAS ABOVE ATMOSPHERIC PRESSURE WHILE PASSING SAID METAL THROUGH A PLURALITY OF ZONES IN A CLOSED SYSTEM, SAID ZONES BEING CAPABLE OF ISOLATION FROM EACH OTHER; MAINTAINING A RELATIVELY DEEP BODY OF MOLTEN METAL IN EACH OF SAID ZONES DURING THE TREATMENT OF SAID METAL THEREIN; INTERMITTENTLY FEEDING CHARGES OF VACUUM-SURFACE-DEGASIFIED, PREHEATED SOLID METAL TO THE FIRST OF SAID ZONES INTO THE BODY OF MELT MAINTAINED THEREIN; TRANSFERRING PORTIONS OF MOLTEN METAL UNDER INERT GAS PRESSURE FROM ZONE TO ZONE, SAID ZONES BEING ISOLATED FROM ONE ANOTHER DURING TREATMENT OF THE METAL THEREIN, WITHDRAWING PORTIONS OF THE TREATED METAL FROM THE LAST OF SAID ZONES; AND TREATING SAID MOLTEN 